Explosionproof plug receptacle



Dec. 16, 1941. SPRAGUE 2,266,663

EXPLOSIONPROOF PLUG RECEPTACLE Filed April 6, 1958 3 Sheets-Sheet lENOCH K. SPRAGUE ATTORNEYS Dec. 16, 1941. E. K. SPRAGUE EXPLOSIONPROOFPLUG RECEPTACLE Filed April 6, 1938 5 Sheets-Sheet 2 gnuc'nl'o'n ENOCHK. SPRAGUE Dec. 16, 1941. 1-:. K. SPRAGUE EXPLOSIONPROOF PLUG RECEPTACLEFiled April 6, 1938 3 Sheets-Sheet 3 NmVunH oo L anon MM ENOCH K.SPRAGUE ATTORNEYS Patented Dec. 16, 1941 UNITED STATES PATENT OFFICE 10Claims.

This invention relates to explosion-proof plug receptacles of the typewherein a plug-in connection may be made without the danger of the partsbeing blown apart by an explosion which may take place.

Under certain circumstances the insertion of a plug in a receptacle whenmaking an electrical connection presents very serious hazards. Forexample, in grain elevators, or in other places where dust is likely toaccumulate, or in 'factories where an accumulation of gases is possible,the making of an electrical connection is extremely hazardous becauseofthe fact that the are caused by the electrical contact will ignite thedust or gases with an explosive violence. While this explosion may belocal in character and confined to the receptacle, it has been at timesviolent enough to blow the plug from the receptacle so that the plug hasseriously injured the worker inserting the plug therein.

It is an object of this invention to make a plug receptacle in which thedanger of creating an electrical are on insertion of the plug issubstantially eliminated.

Another object of this invention is to make a plug receptacle so that atthe time when an arc could be created, the plug is locked againstoutward movement and thus the danger of flying parts is avoided.

A further object of the invention is to make a plug receptacle in whichthe plug must be in serted and locked against outward movement before aswitch is actuated to effect an electrical contact. H

lhe objects of the invention are in general obtained by forming areceptacle enclosing a mercury switch, and supplying means to lock theplug to the receptacle before the mercury switch can be closed. This isdone by attaching the switch to an auxiliary plug body, which body hasspring contact blades engaging the plug proper. The arrangement is suchthat the plug must be inserted simultaneously into the auxiliary plugand locked to the-base receptacle before'the switch is turned to createan electrical circuit between the plug and the auxiliary plug. In thisway, should an arc be caused, the plug cannot be blown outwardly,because it has first been locked to the receptacle. Furthermore, thechances of an are forming are substantially eliminated as contact ismade between metal blade parts before the fluid mercury in its sealedvessel flows to establish the electrical circuit.

The m ans by which these and other objects of my invention are obtainedare more fully set forth in the following description of the inventiontaken in connection with the accompanying drawings, in which:

Fig. 1 is a side view partially in elevation, of the invention with allparts assembled, and the mercury switch in closed position.

Fig. 2 is a front View of the receptacle with the plug removed.

Fig. 3 is a cross-sectional view of the plug member on the line 3--3 ofFig. 1.

Fig. 4 is an end View of the receptacle box shown in Fig. l with aportion of the bottom plate removed to show the switch mechanism.

Fig. 5 is an enlarged detailed view of the plug locking mechanism of'thereceptacle.

Fig. 6 is a side view of the plug member locked to the receptacleportion of Fig. 5.

Figs. 7, 8, and 9 are side views, partially in section, of the plug, thetop of the receptacle, and the auxiliary plug member, respectively,shown in exploded relation.

In Fig. 1, the device is shown generally at A secured to a vertical wallB through any convenient means, such as a bolt C. The device is shownconnected to a conduit D, and may be supported entirely thereby in lieuof the fastening means C. The device is formed of three units, which arethe plug member 2, the auxiliary plug member 4, and the base receptacle6.

The plug, note particularly Figs. 6 and '7, is constructed of a strongmaterial such as cast metal, or it may be of any sufficiently strongmaterial as will resist explosive stresses, and has a body portion 8extended on one end into an annular portion l0. On the end opposite theportion I0 is an opening adapted to receive conductors [2 which are heldby a jam nut l4, preferably formed of brass. The conductors are passedthrough an insulating plate l5 inset into the body 8, said conductorsbeing fastened to the bases of contact prongs l3. Insulating plate l6may be conveniently secured to the body portion 8 by bolts 20, and thecontact prongs I3 are secured to the insulating piece l6 by screws 22.Projecting inwardly of the annular member ID on opposite sides thereofare hardened steel pins 24 which have a locking function as will laterbe described.

The base receptacle 6 is in the form of a box having integral bottomsand sides and preferably being constructed of a strong ferrous material.The top of the box has inwardly extending flanges 36 to which is secureda cover member 32 by means of screws 34. The contacting surfaces of theflanges 30 and the cover 32 are ground, or machined, to make a veryclose, gastight joint, and thus to prevent the spread of fire, or chanceof a secondary explosion being caused by gas or flame leakage, in theevent of explosion within the receptacle 6. Likewise, the joint betweenthe annular portion !6 and the cover 32 is formed of contacting groundfaces. One end of the box is provided with a threaded opening 35 for thesecuring of the box to a pipe line or conduit D, and through whichelectrical conductors are lead into the box.

Disposed on the cap member 32 and rigidly secured thereto is an annularmember 36 which is of such a size as will enable it to engagetelescopically the annular member [6 on the plug 2. Bayonet slots arecut in the walls of annular member 36 to provide longitudinallyextending portions 38 and horizontally extending portions 46, thesebayonet slots being in size and number so as tobe engaged by the pins 24in the annular member ID. At this point it is noted that the plug 2 cantelescopically engage the annular member 36 only by sliding the pins 24through the openings 38, and said plug is locked to the annular member36 by rotating the plug so that the pins are locked in the horizontallyextended portions 46 of the bayonet slots A close joint is obtainedbetween plug 2 and cover 32 by reason of the ground surfaces on the partl6 and the cover 32. On the side of cap piece 32 opposite that uponwhich the annular member 36 is mounted, are projecting lugs 42 and 44,the lug 42 being a straight piece and the lug 44 being a Z-shaped memberto form an opening 46 wider than the opening 48 for a purpose laterdescribed.

Telescopically fitting within the annular member 36 is the auxiliaryplug member 4. This auxiliary plug member is formed of molded insulatingmaterial and carries therein spring contact blades 56 which are adaptedto be engaged by the blades I6 located in the plug piece 2 so as toestablish an electrical contact between these two plug members. One ofthese blades is connected to a lead 52, which lead extends to the supplyline connected with the base box 6. The other lead 54 is connected tothe mercury switch.

The end of the auxiliary plug facing the cap member 2 has eccentricallyinset therein a pilot pin 56, which pilot pin telescopically engages acomplementary recess 56 in the plug 2, when the parts are assembled, sothat a rotation of the plug member 2 wil1 cause a like rotation of theauxiliary plug member. To the opposite end of the auxiliary plug 4 issecured, as by being molded therewith, a base 59 from which projects anarm 66 sufficiently beyond the body portion of the auxiliary plug so asto be adapted to engage the spaces 4-6 and 48 lying between theprojections 42 and 44. The same end of the auxiliary plug 4 has alongitudinal projection 62, which projection in assembled relation mayat some times bear against the base of the box 6 and therefore has arounded end 64 to minimize friction. As shown in Fig. 1, a spring 66surrounds the projection 62 and presses the auxiliary plug 2 outwardlyof the receptacle toward the plug 2.

Mercury switch 16 is of conventional type and includes a body of mercurywithin a closed and sealed vessel and is secured to arm 66 by a bracket72, which is adjustably secured to the arm 66 at 76 by means of a boltand slot construction. As previously stated, lead wire 52 has beenconnected with one of the spring contact blades 56. The

other spring contact blade is connected through lead 54 to the mercuryswitch.

The assembly and operation of the device are as follows: Base member 2,auxiliary plug'4, and cap piece 32 are assembled as a unit by placingthe spring 66 over the projection 62, attaching the mercury switch bymeans of the bracket 12 to the arm 66, and placing them in the box. Cappiece 32 is bolted down to the side of the box, with the annular member36 surrounding the auxiliary plug 4, and the arm 66 extending betweenthe projections 42 and 44 into the space 48, it being noted that thespring 66 presses the auxiliary plug against the cap piece 32 so thatthe end of the arm lies in the space 46. In this position, when themercury switch is mounted on a wall and the plug 2 not yet inserted, theswitch is open and no electrical contacts are established so thatcurrent can flow through the device.

The plug 2 is inserted over the annular member 36 with the pins 24engaging the slots 38 and the blades 16 engaging the blades 56, and asthe plug becomes completely telescopically engaged, the pilot pin 56 onauxiliary plug 4 enters into its corresponding hole 58. It is to benoted at this time that normally the end of the auxiliary plug 4projects beyond the annular member 36 so that the auxiliary plug ispressed further within the base receptacle against the spring 66 as theplug 2 is being engaged thereby. Likewise, it is noted that although thecontact blades 16 and 56 are brought into engagement with each other, nocurrent flows through these contacts as the mercury switch is still inopen position.

When the plug has been inserted to its fullest extent over the annularmember 36, it is rotated to make the pins 24 engage in the horizontallyextending portions of the bayonet slots. As soon as this rotation isstarted, the pins 24 hold the plug 2 against any disengaging oroutwardly moving movement. At the same time, this movement, by virtue ofthe engagement of the pin 56 in hole 56, rotates the arm 66 carrying themercury switch 4'6, the inward movement of the auxiliary plug 4 havingcaused the end of the arm 66 to leave the space 48 and enter into thespace 46 between the projections 42 and 44, respectively. Thereupon, thearm 66 is angularly turned until it engages the free end of theprojection 44. The mercury switch is tilted by this rotation and therebyforms an electrical circuit. This circuit is not formed until the pins24 have locked the plug 2 with the horizontal portions 46 of the bayonetslot. Therefore, it is seen that should any arc be caused by thecreation of the electrical circuit through the action of the mercuryswitch and an explosion created thereby, all the movable parts arefirmly interlocked with each other so that they cannot be separated. Itis by reason of having the plug 2 locked with the annular member 36 thatany explosion will not cause an outward movement of the plug 2, andconsequently, the danger of having a flying part moved by an explosiveforce is avoided. Likewise, it is insured that the switch cannot beclosed until the parts have been interlocked with one another and.therefore danger of faulty or careless operation is avoided.

On withdrawal of the plug 2, the same must first be rotated to bring thepins 24 into the slots 36. This rotation again causes a rotation of thearm 66 and opens the mercury switch before the pins 24 reach the slots38. Consequently, should an explosion occur, the plug 2 is still heldinterlocked with the annular member 36. As the plug 2 is removed and thecontact between the contact prongs I B and 50 broken, no arc will occur,as the current has been previously cut off through the action of themercury switch. When the plug 2 is entirely removed, the spring 66forces the auxiliary plug outward and causes the arm 68 to be re-engagedby the space 48 so that the auxiliary plug and the mercury switch cannotbe again operated until the plug 2 is again properly used.

Should the mercury switch become out of alignment, the position of thesame can be easily adjusted by means of the adjustable clamp '12.

Having now described the structure with which the objects and advantagesof the invention are obtained, what is claimed is:

1. A plug receptacle comprising a removable plug, an auxiliary plug, anda base member, means to lock said removable plug to said base member,means to form metallic contacts between said removable plug and saidauxiliary plug, switch means carried by said auxiliary plug, meansconnecting said switch means with said metallic contacts, and meansindependent of said removable plug locking means for preventing theclosing of said switch means until after said removable plug has beenlocked to said base member.

2. A plug receptacle comprising a removable plug, a base, and anauxiliary rotatable plug, switch means mounted upon and movable withsaid auxiliary plug, means for looking said removable plug to said basemember, means for engaging said removable plug with said auxiliary plug,means for locking said switch means against rotation with respect tosaid base member, and means for rotating said switch means while saidremovable plug is locked to said base.

3. In a plug receptacle, a removable plug having an annular flange onone end thereof, first contact blades projecting into the space boundedby said flange, and leads connected to said blades; a base receptaclehaving a cover plate, an annular member joined to said cover plate andadapted to engage telescopically within said annular flange on saidplug; an auxiliary plug telescopically engaged with said annular memberand extending into said receptacle, resilient means for urging saidauxiliary plug toward said cover plate, an arm secured to said auxiliaryplug, a switch fastened to said arm, second contact blades within saidauxiliary plug adapted to engage said first contact blades, conductormean connecting said second blades and said switch in series; means forlocking said plug to said annular member, means for rotating saidauxiliary plug while looking said plug to said annular member, and meansfor establishing an electrical circuit through said switch after saidplug has been locked to said member.

1. In a plug receptacle as in claim 3, said means for locking said plugto said. annular member comprising pins extending from said annularflange and corresponding bayonet slots in said annular member.

5. In a plug receptacle as in claim 3, a first lug connected to saidcover plate, a Z-shaped lug spaced from said first lug and connected tosaid cover plate, said auxiliary plug being movable against saidresilient means to allow said arm to move from a stop position betweenone portion of each of said lugs to a stop position between anotherportion of said lugs.

6. In a plug receptacle as in claim 3, a pilot pin in one plug and acomplementary recess in the other plug, said pin being engageable withsaid recess upon engagement of said blades.

7. In a plug receptacle as in claim 3, stop means engaging said arm, andmeans for moving said arm from said stop means on locking said removableplug to said annular member.

8. In the combination of a base receptacle, an auxiliary plug in saidreceptacle, a switch operable upon turning of said auxiliary plug, and aremovable plug adapted to be connected to said auxiliary plug, theimprovement comprising means mounting said auxiliary plug in saidreceptacle both for rotation and for movement in the direction of themovement of connection of said auxiliary plug with said removable plug,and means for locking said auxiliary plug against rotation until aftersaid auxiliary plug has been moved in said direction to complete contactbetween said auxiliary plug and said removable plug.

9. In the combination of claim 8, means for locking said removable plugto said receptacle upon rotation of said removable plug to rotate saidauxiliary plug.

10. In the combination of claim 8, said switch comprising a mercuryswitch mounted upon said auxiliary plug for turning movement therewith.

ENOCH K. SPRAGUE.

